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https://issues.apache.org/jira/browse/ACCUMULO-625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13552870#comment-13552870
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An commented on ACCUMULO-625:
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Currently there's a UniqueColumn map/reduce example
(org.apache.accumulo.examples.simple.mapreduce.UniqueColumns). Ideally I would
like to take that example and turn it into an iterator. Due to the tear up and
tear down factor, is it safe to assume i can only perform this operation per
row bases? So the iterator would find all the distinct column in a single row
and the client would have to perform a final distinct for all the rows?
> consider augmenting session state with "breadcrumbs"
> ----------------------------------------------------
>
> Key: ACCUMULO-625
> URL: https://issues.apache.org/jira/browse/ACCUMULO-625
> Project: Accumulo
> Issue Type: Improvement
> Components: tserver
> Reporter: Eric Newton
> Assignee: Keith Turner
>
> Presently, the iterator stack can be created and destroyed at the whim of the
> tserver and its buffering needs. In complex iterations, lower-level
> iterators can make significant progress which is not inherently obvious in
> any returned key. When the iterator stack is re-created to continue a query,
> the last key returned is used to {{seek()}} the iterators. Lower-level
> iterators must re-scan their data to move back to the old position.
> Consider a mechanism to save progress beyond the last key returned.
>
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